Method of fabricating thin film cells and printed circuit boards containing thin film cells using a screen printing process

ABSTRACT

Disclosed herein is a thin film cell in which a cell unit is sealed by a polyimide film. Such a cell unit can be obtained by forming an ion-conductive polymer electrolytic layer formed by mixing polyethylene oxide derivatives with lithium salt on a negative-polarity material composed of lithium or a lithium-aluminum metal foil and then forming a layer of a positive-polarity material from composite materials formed by mixing Vanadium oxide and polyethylene oxide derivatives together, on the electrolytic layer, by using a screen printing process. Also disclosed is a printed circuit board with a thin film cell incorporated therein, in which said cell unit is to be mounted on a flexible film substrate, by using a screen printing process. By this invention, the thin film cell and the printed circuit board can be fabricated in a continuous manner by making use of a screen printing process.

This is a Continuation of application Ser. No. 08/196,805 filed Feb. 15,1994, now abandoned, which in turn is a Continuation Application ofapplication Ser. No. 07/928,318 filed Aug. 12, 1992, now abandoned,which in turn is a Division of application Ser. No. 07/654,548, filedFeb. 13, 1991, now U.S. Pat. No. 5,217,828, which is a Division ofapplication Ser. No. 07/514,684, filed Apr. 19, 1990, now U.S. Pat. No.5,035,965.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin film cell and a printed circuitboard having the thin film cell incorporated therein and a method offabricating the thin film cell and printed circuit board.

2. Description of the Related Art

An Mn dry cell and an Ni--Cd cell have conventionally been known ascells suitable for portable use. Each of these cells is composed of apositive electrode, a separator, an electrolyte, a negative electrodeand a packaging material. By way of example, the method of fabricatingan Ni--Cd cell will hereinafter be described. A nickel oxide and acadmium compound are formed on separate nickel-made punched platesubstrates. The thus-formed substrates are used as negative and positiveelectrodes respectively. Caustic potashes as an electrolytic materialare implanted in a spacer made of a porous plastic which is held betweenboth electrodes.

Thus, a nickel-made punched plate having strong rigidity is used as anelectrode substrate and caustic potash solution is employed as anelectrolyte in the conventional Ni--Cd cell. The following problemsarise when trying to make thin flexible Ni--Cd cells or Mn dry cells.

(1) Inferiority in flexibility;

(2) Failure to make thin enough;

(3) Upon deformation of spacer, the spacer breaks and causes a shortcircuit;

(4) There is a potential leakage of liquid; and

(5) It is difficult to fabricate a cell having electrode patterns in adesired or large variety of shapes.

Therefore, rigid-type shapes such as cylinder-type, button-type,coin-type and box-type shapes have principally been employed in theconventional cells. Thus, it has been considered not only difficult torealize thin and flexible cells but also to realize a design of cells ina variety of shapes.

It has also been considered difficult to mount a thin film cell on aprinted circuit board (PCB) for the above-reasons.

The present invention has been completed with a view toward solving theforegoing problems.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide a method whichpermits a continuous fabrication of thin and flexible cells of desiredshapes by disposing an electrically-conductive polymer electrolyte and apositive-polarity material or the like on a surface of a sheet made of anegative-polarity material to form a desired pattern by using a screenprinting process.

It is a second object of the present invention to provide a method forthe fabrication of a printed circuit board on which thin film cells ofdesired shapes are mounted by directly forming thin film cells andwiring circuits on a non-wiring printed circuit board by using a screenprinting process.

In one aspect of this invention, there is thus provided a method for thefabrication of a thin film cell which is formed by disposing anelectrolytic material on a surface of a sheet made of anegative-polarity material, disposing a positive-polarity material onthe electrolytic material and also disposing an electric collector onthe positive-polarity material, comprising the step of:

forming at least one of the negative-polarity material, the electrolyticmaterial and the positive-polarity material by using a screen printingprocess.

In another aspect of this invention, there is provided a method for thefabrication of a printed circuit board with a thin film cellincorporated therein, comprising the steps of:

forming a negative electrode on a substrate;

forming lead terminals and wiring circuits which are to be connected tothe negative electrode on the substrate; and

forming an electrically-conductive polymer electrolyte, a positiveelectrode and an electric collector on the negative electrodesuccessively;

wherein at least one of the negative electrode, the electrolyte, thepositive electrode and the collector, and the wiring circuits are formedby using a screen printing process.

The above first-mentioned fabrication method permits the fabrication ofthin and flexible cells of desired shapes in a continuous line. Theabove second-mentioned fabrication method also permits the fabricationof the printed circuit board with the thin film cells of desired shapes,which are to be incorporated therein.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the inventionwill become more apparent from reading the following description of apreferred embodiment taken in connection with the accompanying drawingsin which;

FIG. 1 schematically illustrates various steps in a method offabricating a thin film cell according to one embodiment of thisinvention;

FIG. 2 is a cross-sectional view of a thin film cell;

FIG. 3 is an enlarged cross-sectional view showing one of said varioussteps of FIG. 1;

FIGS. 4(a) through 4(e) schematically illustrate various procedures inthe fabrication method of a printed circuit board with a thin film cellincorporated therein according to one embodiment of this invention; and

FIG. 5 is a plan view of a printed circuit board.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will hereinafter be made of one embodiment in which amethod according to the present invention is described specifically,with reference to the accompanying drawings.

As shown in FIG. 2, a sheet-like thin film cell 10 which is formed bythe method according to the present invention includes anegative-polarity (anode) material 21 disposed as the lowest layer, anelectrolytic material 22 disposed on the negative-polarity material 21,a positive-polarity (cathode) material 23 disposed on the electrolyticmaterial 22 and an electric current collector 24 placed on thepositive-polarity material 23. The negative-polarity material 21 iscomposed of, for example, lithium (Li) or a metal foil made of a lithiumaluminum alloy (Li--Al). The electrolytic material 22 is composed of,for example, a solid-like polyelectrolyte. The positive-polaritymaterial 23 is made up of, for example, composite materials (which areobtained by synthesizing resin and powder made of inorganic materials)such as Vanadium oxide (V₆ O₁₃). The electric collector 24 consists of,for example, a nickel (Ni)-made metal foil.

A method of fabricating a thin film cell will hereinafter be describedwith reference to FIG. 1. A commercially available Li--Al metal foil,which has been wound in a roll form, is delivered to the inside of aclean room 11 (the degree of cleanness may preferably be about 100) by aconveyor-line system, followed by subjecting the same to ultrasoniccleaning under the presence of an organic solvent such as kerosene andthe metal foil is then cleaned by a brush detergent action or the like,in a cleaning apparatus 2. An ion electrically-conductive polymerelectrolyte obtained by mixing, for example, polyethylene oxidederivatives with lithium (Li) salt in a conductive-polymerpolymerization apparatus 3b is automatically supplied on a plate with adesired pattern formed thereon in a screen printing apparatus 3a and theelectrolytes are then applied on the metal foil 1. This portion of themetal foil is next dried by an ultraviolet (UV) calcining oven 4.

The above-described screen printing apparatus 3a may preferably havemeshes of about #200 to #500, a squeegee speed of 10-30 mm/sec.,squeegee angle of 10°-20° squeegee hardness of 600°-80°, printingpressure of 1.0-2.0 kg/cm² and clearance between each mesh and a printedmatter of about 3.0 mm. In addition, the viscosity of the polymer to beused in the screen printing apparatus 3a is set at about 30,000 CPS. Thecondition of calcining of the metal foil at the oven 4 may preferably beabout 100-1,000 mJ/cm².

A positive-polarity material obtained by mixing Vanadium oxide V₆ O₁₃and the aforementioned polyethylene oxide derivatives together, saidmaterial optionally having carbon powder added thereto as needed by apositive-polarity material mixing apparatus 5b, is next applied on theabove-described polymer electrolyte by a screen printing apparatus 5awhich is similar to that described above (3a). The positive-polaritymaterial, which has been applied in desired patterns, enters a calciningoven 6 in the same manner as described above to be hardened therein. Theconditions of the screen printing and of the calcining at the oven arethe same as that described above.

An electric collector composed of carbon paste, silver paste, copperpaste or the like and shield agents or the like, which are mixed byusing a collector mixing apparatus 7b, is then applied in desiredpatterns by making use of another screen printing apparatus 7a.Thereafter, such a product is calcined by a calcining oven 8 in the samemanner as described above. The conditions of the printing and calciningare the same as that described above. The thus-obtained patterns arenext cut by using a pattern cutting apparatus 9 to form each of theflexible thin-film cell units 10.

Although the described example utilizes a negative-polarity foil andforms the positive-polarity layer by using a screen printing process, itis understood that a positive-polarity foil can alternatively be used inwhich case the negative-polarity layer is formed by a screen printingprocess. Additionally, while only the electric collector 7 has beendescribed as being formed from a conductive paste, it is understood thatthe positive and negative polarity materials as well as the electrolyticmaterial can also be formed from a conductive paste.

As shown in FIG. 3, packaging materials 12 and 13 are next brought intoa laminated state with the thin-film cell unit 10. Each of packagingmaterials 12 and 13 are composed of, for example, polyimide and includelead terminals 17 formed of copper, aluminum, etc. Thereafter, theresultant products are each hot-bonded by a hot-bonding apparatus 14 andone end portion of each of the sheet-like cells is then fusion-bonded,while performing a vacuum-draw. The sheet-like cells are cut into apredetermined size by a cut-to-size apparatus 15 to obtain each of theflexible thin-film cells 16.

The above-described steps represent a method for the fabrication offlexible thin-film cells of a single-layer structure. However, in orderto produce a multi-layer structure it is only necessary to return thecell unit (which includes the negative-polarity material layer,electrolyte layer and positive-polarity material layer) to the firststep, before forming the collector and performing lamination withpackaging material, to thermally fusion-bond the Li--Al foil onto thepositive-polarity material layer, followed by superposition of each ofthe layers one on top of another successively in a similar manner asdescribed above. After the desired number of layers are formed, anelectric collector is formed on the last formed positive-polaritymaterial layer and the entire cell is laminated by the packagingmaterial.

A description will next be made of a method for the fabrication of aprinted circuit board with a thin film cell incorporated therein withreference to FIG. 4. Epoxy resin adhesive 52 shown in FIG. 4(b) isapplied, at a desired position, on a polyester (Mylar) film 51 depictedin FIG. 4(a) by using the screen printing process. While in an uncuredstate, a negative-polarity material 53 made up of the Li--Al foil, whichhas been punched to a desired shape, is disposed on the adhesive 52, tothereby fixedly secure the same thereon. As shown in FIG. 4(c), leadterminals and necessary wiring circuits 54 connected to each of negativeelectrodes of cells are formed by making use of carbon paste, silverpaste, copper paste and any other electrically-conductive paste inaccordance with the screen printing process. After they have calcined,an ion-conductive polymer electrolyte 55 obtained by mixing polyethyleneoxide derivatives with lithium (Li) salt is applied by the screenprinting process in order to form a desired pattern as shown in FIG.4(d). After calcining of the resultant product, an insulating resist 56such as polyimide, which is adapted to prevent short-circuiting betweena positive-polarity material to be formed subsequently and each of thenegative-polarity lead terminals, is formed. As illustrated in FIG.4(e), a positive-polarity material 57 obtained by mixing Vanadium oxideV₆ O₁₃ and polyethylene oxide derivatives together, said materialoptionally having carbon powder added thereto as needed, is next appliedon the above-described polymer electrolyte 55 so as to obtain a desiredshape in the same manner as described above by using the screen printingprocess, followed by subjecting of the same to calcining. Next, carbonpaste, silver paste, copper paste, etc. is applied on the desiredpattern to form an electric collector 58 by using the screen printingprocess, followed by subjecting of the same to calcining.

FIG. 5 shows one example of a printed circuit board with the thin filmcells incorporated therein, which has been fabricated in theabove-described manner. Mounted on printed circuit board 100 are a 3-Vcell 101, a 6-V cell 102, a 12-V cell 103, each fabricated by theabove-described method, ICs (Integrated Circuits) 104, mini-flat ICs105, etc. In order to obtain the cells referred to above, that producedifferent output power, it is only necessary to increase or decrease thepositive and negative polarity materials and the capacity of each of theelectrolytic layers, which constitute each of the cells, in thefabrication method shown in FIG. 4.

While the present invention has been described in its preferredembodiment, it is to be understood that the invention is not restrictedto the specific embodiment disclosed herein. Various changes,modifications and improvements may be made in the invention which do notaffect the spirit of the invention nor exceed the scope thereof asexpressed in the appended claims.

What is claimed is:
 1. A method of fabricating a thin film cell,comprising:using a screen printing process, forming an electrolyticmaterial layer on a flexible, electrically-conductive foil layer, saidfoil layer having a polarity such that said foil layer is an anodelayer; and using a screen printing process, forming a cathode layer onsaid electrolytic material layer.
 2. The method according to claim 1,further comprising surrounding said anode layer, electrolytic layer, andcathode layer by a packaging member.
 3. The method according to claim 2,wherein said packaging member includes a first and a second sheet ofheat-bondable, insulative material containing a lead terminal andwherein said first sheet is placed below said anode layer, said secondsheet is placed above said cathode layer and said first and secondsheets are vacuum fusion bonded to each other.
 4. The method accordingto claim 1, further comprising a fourth step of forming a currentcollector layer on said cathode layer.
 5. The method according to claim1, further comprising:attaching said anode layer on a substrate; andforming lead terminals and a circuit pattern on said substrate whichcontinuously extend from said anode layer.
 6. The method according toclaim 5, further comprising:forming a current collector layer on saidcathode layer.
 7. The method according to claim 6, wherein at least oneof said current collector layer, said lead terminals, and said circuitpattern is formed by a screen printing process.
 8. The method accordingto claim 4, wherein said current collector layer is formed using ascreen printing process.
 9. The method according to claim 1, whereinsaid anode layer is an electrically-conductive metal foil.
 10. Themethod according to claim 9, wherein said metal foil is lithium foil.11. The method according to claim 9, wherein said metal foil is alithium-aluminum alloy foil.
 12. The method according to claim 1,wherein said cathode layer is a composite material obtained by mixingVanadium oxide and polyethylene oxide derivatives together.
 13. A methodof fabricating a thin film cell, said thin film cell having a flexible,electrically-conductive foil layer, an electrolytic material layer andan electrode layer, said foil layer and said electrode layer havingpolarities such that when said foil layer is a cathode layer saidelectrode layer is an anode layer, and when said foil layer is an anodelayer said electrode layer is a cathode layer, said method comprisingthe steps of:using a screen printing process, forming said electrolyticmaterial layer on said flexible, electrically-conductive foil layer; andusing a screen printing process, forming said electrode layer on saidelectrolytic material layer.
 14. The method according to claim 13,wherein said electrolytic material layer is an ion-conductive polymerelectrolyte.
 15. The method according to claim 14, wherein said polymerelectrolyte is formed by mixing polyethylene oxide derivatives withlithium salt.
 16. The method according to claim 15, wherein said polymerelectrolyte further includes carbon powder mixed therein.
 17. The methodaccording to claim 4, wherein said current collector layer is formed byapplying conductive paste on said cathode layer.
 18. The methodaccording to claim 5, wherein said anode layer is attached to saidsubstrate by applying an epoxy resin adhesive to said substrate prior toforming said anode layer.
 19. The method according to claim 6, whereinan insulative layer is formed over a portion of said electrolytic layerprior to formation of said cathode layer for preventing short-circuitingbetween said cathode layer and said lead terminals.
 20. The methodaccording to claim 19, wherein said insulative layer is polyimide. 21.The method according to claim 5, wherein said substrate is a polyesterfilm.
 22. The method of claim 13, wherein the step of forming saidelectrolytic material layer comprises forming said electrolytic materiallayer in a predetermined pattern, andwherein the step of forming saidelectrode layer comprises forming said electrode layer in apredetermined pattern.
 23. A method of fabricating a thin film cell,comprising:using a screen printing process, forming an electrolyticmaterial layer on a flexible, electrically-conductive foil layer, saidfoil layer having a polarity such that said foil layer is a cathodelayer; and using a screen printing process, forming an anode layer onsaid electrolytic material layer.
 24. The method of claim 23, whereinthe step of forming an electrolytic material layer comprises forming theelectrolytic material layer in a predetermined pattern, andwherein thestep of forming an anode layer comprises forming the anode layer in apredetermined pattern.
 25. The method of claim 1, wherein the step offorming an electrolytic material layer comprises forming theelectrolytic material layer in a predetermined pattern, andwherein thestep of forming a cathode layer comprises forming the cathode layer in apredetermined pattern.